The increase of the traffic and of the speeds (TGV, Intercity), the introduction of cadenced timetables have notably increased the stresses to which the rails are submitted and consequently, the deformations of the longitudinal and transverse profiles of the head of the rail.
The timetables which are more and more charged leave for the maintenance of the rails and of the tracks only more and more reduced time intervals. It is thus necessary to proceed to an optimal programming of these works, in order to use fully the intervals at disposition.
Now the determination of the number of passes is empirical, it depends mainly on the experience acquired by comparing the preceeding grinding works. For example, one knows that for a given track, of a given network, presenting a given undulatory wearing off, the number of passes to be made with the usually used machine is of the order of "X". If the transverse profile is no longer perfect, one adds a number "Y" of passes, so that the total will be "X+Y".
Such an empirical practice is no longer possible due to the requirements relative to the quality now required from the reprofiled rails and of the occupation time of the tracks which is always greater.
One knows numerous reprofiling or profiling methods for the rails of a railroad track, as well as of railroad vehicles equiped with devices to make this work as described for example in Swiss patents CH 633.336; CH 654.047; CH 666.068; CH 655.528 and in Swiss patent application CH 817/88. All these methods and these devices do not permit however to program in an optimal way the reprofiling operations of the rails of a railroad track as a function of the type of the machine to be used, and of the occupation rates of the track, of the wearing off state of the rails and of the metal removal capacity of the reprofiling tools.